Multi-gate transistors and memories having multi-gate transistors

ABSTRACT

Transistors, and memories including such transistors, might include an active area having a first conductivity type, first and second source/drain regions in the active area and having a second conductivity type, and a plurality of control gates between the first and second source/drain regions and the second source/drain region, wherein each control gate of the plurality of control gates includes a respective first control gate portion overlying a first side of the active area, and a respective second control gate portion connected to its respective first control gate portion that is either adjacent to a second side of the active area orthogonal to the first side of the active area, or underlying a second side of the active area opposite the first side of the active area.

RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.17/223,482, titled “MULTI-GATE TRANSISTORS, APPARATUS HAVING MULTI-GATETRANSISTORS, AND METHODS OF FORMING MULTI-GATE TRANSISTORS,” filed Apr.6, 2021, (Allowed) which is commonly assigned and incorporated herein byreference.

TECHNICAL FIELD

The present disclosure relates generally to integrated circuits, and, inparticular, in one or more embodiments, the present disclosure relatesto multi-gate transistors, apparatus containing multi-gate transistorsand methods of forming multi-gate transistors.

BACKGROUND

Memories (e.g., memory devices) are typically provided as internal,semiconductor, integrated circuit devices in computers or otherelectronic devices. There are many different types of memory includingrandom-access memory (RAM), read only memory (ROM), dynamic randomaccess memory (DRAM), synchronous dynamic random access memory (SDRAM),and flash memory.

Flash memory has developed into a popular source of non-volatile memoryfor a wide range of electronic applications. Flash memory typically usea one-transistor memory cell that allows for high memory densities, highreliability, and low power consumption. Changes in threshold voltage(Vt) of the memory cells, through programming (which is often referredto as writing) of charge storage structures (e.g., floating gates orcharge traps) or other physical phenomena (e.g., phase change orpolarization), determine the data state (e.g., data value) of eachmemory cell. Common uses for flash memory and other non-volatile memoryinclude personal computers, personal digital assistants (PDAs), digitalcameras, digital media players, digital recorders, games, appliances,vehicles, wireless devices, mobile telephones, and removable memorymodules, and the uses for non-volatile memory continue to expand.

A NAND flash memory is a common type of flash memory device, so calledfor the logical form in which the basic memory cell configuration isarranged. Typically, the array of memory cells for NAND flash memory isarranged such that the control gate of each memory cell of a row of thearray is connected together to form an access line, such as a word line.Columns of the array include strings (often termed NAND strings) ofmemory cells connected together in series between a pair of selectgates, e.g., a source select transistor and a drain select transistor.Each source select transistor might be connected to a source, while eachdrain select transistor might be connected to a data line, such ascolumn bit line. Variations using more than one select gate between astring of memory cells and the source, and/or between the string ofmemory cells and the data line, are known.

In a memory device, access of memory cells (e.g., programming memorycells) often utilizes high voltage levels delivered to the control gatesof those memory cells, which might exceed 20V. Gating such voltagelevels often relies on transistors, such as field-effect transistors(FETs), having high breakdown voltages. Such transistors often utilize arelatively large footprint, and typically require overdrive voltagesapplied to their control gates in order to pass the full voltage levelof a voltage node.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a memory in communication with aprocessor as part of an electronic system, according to an embodiment.

FIGS. 2A-2C are schematics of portions of an array of memory cells ascould be used in a memory of the type described with reference to FIG. 1.

FIG. 3A is a schematic of a portion of an array of memory cells andstring drivers as could be used in a memory device of the type describedwith reference to FIG. 1 .

FIG. 3B is a schematic of a portion of one example of a string driver ascould be used in a memory of the type described with reference to FIG. 1.

FIG. 3C is a schematic of a portion of another example of a stringdriver as could be used in a memory of the type described with referenceto FIG. 1 .

FIG. 4 is a plan view of multi-gate transistors in accordance with anembodiment.

FIGS. 5A-12D are cross-sectional views of the transistors of FIG. 4 atvarious stages of fabrication in accordance with an embodiment.

FIG. 13 is a cross-sectional view of a transistor of FIG. 4 inaccordance with another embodiment.

FIG. 14 is a cross-sectional view of the transistors of FIG. 4 inaccordance with a further embodiment.

FIGS. 15A-15E are cross-sectional views of transistors of FIG. 4 inaccordance with various embodiments.

FIG. 16 conceptually depicts connection of a portion of a string driverconnected to access lines of multiple blocks of memory cells inaccordance with an embodiment.

FIG. 17 is a perspective view of a transistor in accordance with anembodiment.

DETAILED DESCRIPTION

In the following detailed description, reference is made to theaccompanying drawings that form a part hereof, and in which is shown, byway of illustration, specific embodiments. In the drawings, likereference numerals describe substantially similar components throughoutthe several views. Other embodiments might be utilized and structural,logical and electrical changes might be made without departing from thescope of the present disclosure. The following detailed description is,therefore, not to be taken in a limiting sense.

The term “semiconductor” used herein can refer to, for example, a layerof material, a wafer, or a substrate, and includes any basesemiconductor structure. “Semiconductor” is to be understood asincluding silicon-on-sapphire (SOS) technology, silicon-on-insulator(SOI) technology, thin film transistor (TFT) technology, doped andundoped semiconductors, epitaxial layers of a silicon supported by abase semiconductor structure, as well as other semiconductor structureswell known to one skilled in the art. Furthermore, when reference ismade to a semiconductor in the following description, previous processsteps might have been utilized to form regions/junctions in the basesemiconductor structure, and the term semiconductor can include theunderlying layers containing such regions/junctions.

The term “conductive” as used herein, as well as its various relatedforms, e.g., conduct, conductively, conducting, conduction,conductivity, etc., refers to electrically conductive unless otherwiseapparent from the context. Similarly, the term “connecting” as usedherein, as well as its various related forms, e.g., connect, connected,connection, etc., refers to electrically connecting by a conductive pathunless otherwise apparent from the context.

It is recognized herein that even where values might be intended to beequal, variabilities and accuracies of industrial processing andoperation might lead to differences from their intended values. Thesevariabilities and accuracies will generally be dependent upon thetechnology utilized in fabrication and operation of the integratedcircuit device. As such, if values are intended to be equal, thosevalues are deemed to be equal regardless of their resulting values.

Various embodiments might facilitate high breakdown voltage transistors,e.g., field-effect transistors (FETs), through the use of multiple gatesalong an active area providing a channel region of the transistor. Whiletransistors of various embodiments might be utilized in all types ofintegrated circuit devices utilizing transistors, they will be describedherein with specific reference to apparatus containing memory cells,some of which are commonly referred to as memory devices or simplymemory.

FIG. 1 is a simplified block diagram of a first apparatus, in the formof a memory (e.g., memory device) 100, in communication with a secondapparatus, in the form of a processor 130, as part of a third apparatus,in the form of an electronic system, according to an embodiment. Someexamples of electronic systems include personal computers, personaldigital assistants (PDAs), digital cameras, digital media players,digital recorders, games, appliances, vehicles, wireless devices, mobiletelephones and the like. The processor 130, e.g., a controller externalto the memory device 100, might be a memory controller or other externalhost device.

Memory device 100 includes an array of memory cells 104 that might belogically arranged in rows and columns. Memory cells of a logical roware typically connected to the same access line (commonly referred to asa word line) while memory cells of a logical column are typicallyselectively connected to the same data line (commonly referred to as abit line). A single access line might be associated with more than onelogical row of memory cells and a single data line might be associatedwith more than one logical column. Memory cells (not shown in FIG. 1 )of at least a portion of array of memory cells 104 are capable of beingprogrammed to one of at least two target data states.

A row decode circuitry 108 and a column decode circuitry 110 areprovided to decode address signals. Address signals are received anddecoded to access the array of memory cells 104. Memory device 100 alsoincludes input/output (I/O) control circuitry 112 to manage input ofcommands, addresses and data to the memory device 100 as well as outputof data and status information from the memory device 100. An addressregister 114 is in communication with I/O control circuitry 112 and rowdecode circuitry 108 and column decode circuitry 110 to latch theaddress signals prior to decoding. A command register 124 is incommunication with I/O control circuitry 112 and control logic 116 tolatch incoming commands.

A controller (e.g., the control logic 116 internal to the memory device100) controls access to the array of memory cells 104 in response to thecommands and might generate status information for the externalprocessor 130, i.e., control logic 116 is configured to perform accessoperations (e.g., sensing operations [which might include readoperations and verify operations], programming operations and/or eraseoperations) on the array of memory cells 104. The control logic 116 isin communication with row decode circuitry 108 and column decodecircuitry 110 to control the row decode circuitry 108 and column decodecircuitry 110 in response to the addresses. The control logic 116 mightinclude instruction registers 128 which might represent computer-usablememory for storing computer-readable instructions. For some embodiments,the instruction registers 128 might represent firmware. Alternatively,the instruction registers 128 might represent a grouping of memorycells, e.g., reserved block(s) of memory cells, of the array of memorycells 104.

Control logic 116 might also be in communication with a cache register118. Cache register 118 latches data, either incoming or outgoing, asdirected by control logic 116 to temporarily store data while the arrayof memory cells 104 is busy writing or reading, respectively, otherdata. During a programming operation (e.g., write operation), data mightbe passed from the cache register 118 to the data register 120 fortransfer to the array of memory cells 104; then new data might belatched in the cache register 118 from the I/O control circuitry 112.During a read operation, data might be passed from the cache register118 to the I/O control circuitry 112 for output to the externalprocessor 130; then new data might be passed from the data register 120to the cache register 118. The cache register 118 and/or the dataregister 120 might form (e.g., might form a portion of) a page buffer ofthe memory device 100. A page buffer might further include sensingdevices (not shown in FIG. 1 ) to sense a data state of a memory cell ofthe array of memory cells 104, e.g., by sensing a state of a data lineconnected to that memory cell. A status register 122 might be incommunication with I/O control circuitry 112 and control logic 116 tolatch the status information for output to the processor 130.

Memory device 100 receives control signals at control logic 116 fromprocessor 130 over a control link 132. The control signals might includea chip enable CE #, a command latch enable CLE, an address latch enableALE, a write enable WE #, a read enable RE #, and a write protect WP #.Additional or alternative control signals (not shown) might be furtherreceived over control link 132 depending upon the nature of the memorydevice 100. Memory device 100 receives command signals (which representcommands), address signals (which represent addresses), and data signals(which represent data) from processor 130 over a multiplexedinput/output (I/O) bus 134 and outputs data to processor 130 over I/Obus 134.

For example, the commands might be received over input/output (I/O) pins[7:0] of I/O bus 134 at I/O control circuitry 112 and might then bewritten into command register 124. The addresses might be received overinput/output (I/O) pins [7:0] of I/O bus 134 at I/O control circuitry112 and might then be written into address register 114. The data mightbe received over input/output (I/O) pins [7:0] for an 8-bit device orinput/output (I/O) pins [15:0] for a 16-bit device at I/O controlcircuitry 112 and then might be written into cache register 118. Thedata might be subsequently written into data register 120 forprogramming the array of memory cells 104. For another embodiment, cacheregister 118 might be omitted, and the data might be written directlyinto data register 120. Data might also be output over input/output(I/O) pins [7:0] for an 8-bit device or input/output (I/O) pins [15:0]for a 16-bit device. Although reference might be made to I/O pins, theymight include any conductive nodes providing for electrical connectionto the memory device 100 by an external device (e.g., processor 130),such as conductive pads or conductive bumps as are commonly used.

It will be appreciated by those skilled in the art that additionalcircuitry and signals can be provided, and that the memory device 100 ofFIG. 1 has been simplified. It should be recognized that thefunctionality of the various block components described with referenceto FIG. 1 might not necessarily be segregated to distinct components orcomponent portions of an integrated circuit device. For example, asingle component or component portion of an integrated circuit devicecould be adapted to perform the functionality of more than one blockcomponent of FIG. 1 . Alternatively, one or more components or componentportions of an integrated circuit device could be combined to performthe functionality of a single block component of FIG. 1 .

Additionally, while specific I/O pins are described in accordance withpopular conventions for receipt and output of the various signals, it isnoted that other combinations or numbers of I/O pins (or other I/O nodestructures) might be used in the various embodiments.

FIG. 2A is a schematic of a portion of an array of memory cells 200A,such as a NAND memory array, as could be used in a memory of the typedescribed with reference to FIG. 1 , e.g., as a portion of array ofmemory cells 104. Memory array 200A includes access lines (e.g., wordlines) 202 ₀ to 202 _(N), and data lines (e.g., bit lines) 204 ₀ to 204_(M). The access lines 202 might be connected to global access lines(e.g., global word lines), not shown in FIG. 2A, in a many-to-onerelationship. For some embodiments, memory array 200A might be formedover a semiconductor that, for example, might be conductively doped tohave a conductivity type, such as a p-type conductivity, e.g., to form ap-well, or an n-type conductivity, e.g., to form an n-well.

Memory array 200A might be arranged in rows (each corresponding to anaccess line 202) and columns (each corresponding to a data line 204).Each column might include a string of series-connected memory cells(e.g., non-volatile memory cells), such as one of NAND strings 206 ₀ to206 _(M). Each NAND string 206 might be connected (e.g., selectivelyconnected) to a common source (SRC) 216 and might include memory cells208 ₀ to 208 _(N). The source 216 might represent a voltage nodecommonly selectively connected to the memory cells 208 of a plurality ofNAND strings 206. The memory cells 208 might represent non-volatilememory cells for storage of data. The memory cells 208 ₀ to 208 _(N)might include memory cells intended for storage of data, and mightfurther include other memory cells not intended for storage of data,e.g., dummy memory cells. Dummy memory cells are typically notaccessible to a user of the memory, and are instead typicallyincorporated into the string of series-connected memory cells foroperational advantages that are well understood.

The memory cells 208 of each NAND string 206 might be connected inseries between a select gate 210 (e.g., a field-effect transistor), suchas one of the select gates 210 ₀ to 210 _(M) (e.g., that might be sourceselect transistors, commonly referred to as select gate source), and aselect gate 212 (e.g., a field-effect transistor), such as one of theselect gates 212 ₀ to 212 _(M) (e.g., that might be drain selecttransistors, commonly referred to as select gate drain). Select gates210 ₀ to 210 _(M) might be commonly connected to a select line 214, suchas a source select line (SGS), and select gates 212 ₀ to 212 _(M) mightbe commonly connected to a select line 215, such as a drain select line(SGD). Although depicted as traditional field-effect transistors, theselect gates 210 and 212 might utilize a structure similar to (e.g., thesame as) the memory cells 208. The select gates 210 and 212 mightrepresent a plurality of select gates connected in series, with eachselect gate in series configured to receive a same or independentcontrol signal.

A source of each select gate 210 might be connected to common source216. The drain of each select gate 210 might be connected to a memorycell 208 ₀ of the corresponding NAND string 206. For example, the drainof select gate 210 ₀ might be connected to memory cell 208 ₀ of thecorresponding NAND string 206 ₀. Therefore, each select gate 210 mightbe configured to selectively connect a corresponding NAND string 206 tocommon source 216. A control gate of each select gate 210 might beconnected to select line 214.

The drain of each select gate 212 might be connected to the data line204 for the corresponding NAND string 206. For example, the drain ofselect gate 212 ₀ might be connected to the data line 204 ₀ for thecorresponding NAND string 206 ₀. The source of each select gate 212might be connected to a memory cell 208 _(N) of the corresponding NANDstring 206. For example, the source of select gate 212 ₀ might beconnected to memory cell 208 _(N) of the corresponding NAND string 206₀. Therefore, each select gate 212 might be configured to selectivelyconnect a corresponding NAND string 206 to the corresponding data line204. A control gate of each select gate 212 might be connected to selectline 215.

The memory array in FIG. 2A might be a quasi-two-dimensional memoryarray and might have a generally planar structure, e.g., where thecommon source 216, NAND strings 206 and data lines 204 extend insubstantially parallel planes. Alternatively, the memory array in FIG.2A might be a three-dimensional memory array, e.g., where NAND strings206 might extend substantially perpendicular to a plane containing thecommon source 216 and to a plane containing the data lines 204 thatmight be substantially parallel to the plane containing the commonsource 216.

Typical construction of memory cells 208 includes a data-storagestructure 234 (e.g., a floating gate, charge trap, or other structureconfigured to store charge) that can determine a data state of thememory cell (e.g., through changes in threshold voltage), and a controlgate 236, as shown in FIG. 2A. The data-storage structure 234 mightinclude both conductive and dielectric structures while the control gate236 is generally formed of one or more conductive materials. In somecases, memory cells 208 might further have a defined source/drain (e.g.,source) 230 and a defined source/drain (e.g., drain) 232. Memory cells208 have their control gates 236 connected to (and in some cases form)an access line 202.

A column of the memory cells 208 might be a NAND string 206 or aplurality of NAND strings 206 selectively connected to a given data line204. A row of the memory cells 208 might be memory cells 208 commonlyconnected to a given access line 202. A row of memory cells 208 can, butneed not, include all memory cells 208 commonly connected to a givenaccess line 202. Rows of memory cells 208 might often be divided intoone or more groups of physical pages of memory cells 208, and physicalpages of memory cells 208 often include every other memory cell 208commonly connected to a given access line 202. For example, memory cells208 commonly connected to access line 202 _(N) and selectively connectedto even data lines 204 (e.g., data lines 204 ₀, 204 ₂, 204 ₄, etc.)might be one physical page of memory cells 208 (e.g., even memory cells)while memory cells 208 commonly connected to access line 202 _(N) andselectively connected to odd data lines 204 (e.g., data lines 204 ₁, 204₃, 204 ₅, etc.) might be another physical page of memory cells 208(e.g., odd memory cells). Although data lines 204 ₃-204 ₅ are notexplicitly depicted in FIG. 2A, it is apparent from the figure that thedata lines 204 of the array of memory cells 200A might be numberedconsecutively from data line 204 ₀ to data line 204 _(M). Othergroupings of memory cells 208 commonly connected to a given access line202 might also define a physical page of memory cells 208. For certainmemory devices, all memory cells commonly connected to a given accessline might be deemed a physical page of memory cells. The portion of aphysical page of memory cells (which, in some embodiments, could stillbe the entire row) that is read during a single read operation orprogrammed during a single programming operation (e.g., an upper orlower page of memory cells) might be deemed a logical page of memorycells. A block of memory cells might include those memory cells that areconfigured to be erased together, such as all memory cells connected toaccess lines 202 ₀-202 _(N) (e.g., all NAND strings 206 sharing commonaccess lines 202). Unless expressly distinguished, a reference to a pageof memory cells herein refers to the memory cells of a logical page ofmemory cells.

Although the example of FIG. 2A is discussed in conjunction with NANDflash, the embodiments and concepts described herein are not limited toa particular array architecture or structure, and can include otherstructures (e.g., SONOS or other data storage structure configured tostore charge) and other architectures (e.g., AND arrays, NOR arrays,etc.).

FIG. 2B is another schematic of a portion of an array of memory cells200B as could be used in a memory of the type described with referenceto FIG. 1 , e.g., as a portion of array of memory cells 104. Likenumbered elements in FIG. 2B correspond to the description as providedwith respect to FIG. 2A. FIG. 2B provides additional detail of oneexample of a three-dimensional NAND memory array structure. Thethree-dimensional NAND memory array 200B might incorporate verticalstructures which might include semiconductor pillars where a portion ofa pillar might act as a channel region of the memory cells of NANDstrings 206. The NAND strings 206 might be each selectively connected toa data line 204 ₀-204 _(M) by a select transistor 212 (e.g., that mightbe drain select transistors, commonly referred to as select gate drain)and to a common source 216 by a select transistor 210 (e.g., that mightbe source select transistors, commonly referred to as select gatesource). Multiple NAND strings 206 might be selectively connected to thesame data line 204. Subsets of NAND strings 206 can be connected totheir respective data lines 204 by biasing the select lines 215 ₀-215_(K) to selectively activate particular select transistors 212 eachbetween a NAND string 206 and a data line 204. The select transistors210 can be activated by biasing the select line 214. Each access line202 might be connected to multiple rows of memory cells of the memoryarray 200B. Rows of memory cells that are commonly connected to eachother by a particular access line 202 might collectively be referred toas tiers.

The three-dimensional NAND memory array 200B might be formed overperipheral circuitry 226. The peripheral circuitry 226 might represent avariety of circuitry for accessing the memory array 200B. The peripheralcircuitry 226 might include complementary circuit elements. For example,the peripheral circuitry 226 might include both n-channel and p-channeltransistors formed on a same semiconductor substrate, a process commonlyreferred to as CMOS, or complementary metal-oxide-semiconductors.Although CMOS often no longer utilizes a strictmetal-oxide-semiconductor construction due to advancements in integratedcircuit fabrication and design, the CMOS designation remains as a matterof convenience.

FIG. 2C is a further schematic of a portion of an array of memory cells200C as could be used in a memory of the type described with referenceto FIG. 1 , e.g., as a portion of array of memory cells 104. Likenumbered elements in FIG. 2C correspond to the description as providedwith respect to FIG. 2A. Array of memory cells 200C might includestrings of series-connected memory cells (e.g., NAND strings) 206,access (e.g., word) lines 202, data (e.g., bit) lines 204, select lines214 (e.g., source select lines), select lines 215 (e.g., drain selectlines) and source 216 as depicted in FIG. 2A. A portion of the array ofmemory cells 200A might be a portion of the array of memory cells 200C,for example. FIG. 2C depicts groupings of NAND strings 206 into blocksof memory cells 250, e.g., blocks of memory cells 250 ₀-250 _(L). Blocksof memory cells 250 might be groupings of memory cells 208 that might beerased together in a single erase operation, sometimes referred to aserase blocks. Each block of memory cells 250 might include those NANDstrings 206 commonly associated with a single select line 215, e.g.,select line 215 ₀. The source 216 for the block of memory cells 250 ₀might be a same source as the source 216 for the block of memory cells250 _(L). For example, each block of memory cells 250 ₀-250 _(L) mightbe commonly selectively connected to the source 216. Access lines 202and select lines 214 and 215 of one block of memory cells 250 might haveno direct connection to access lines 202 and select lines 214 and 215,respectively, of any other block of memory cells of the blocks of memorycells 250 ₀-250 _(L).

The data lines 204 ₀-204 _(M) might be connected (e.g., selectivelyconnected) to a buffer portion 240, which might be a portion of a databuffer of the memory. The buffer portion 240 might correspond to amemory plane (e.g., the set of blocks of memory cells 250 ₀-250 _(L)).The buffer portion 240 might include sensing devices (not shown in FIG.2C) for sensing data values indicated on respective data lines 204.

While the blocks of memory cells 250 of FIG. 2C depict only one selectline 215 per block of memory cells 250, the blocks of memory cells 250might include those NAND strings 206 commonly associated with more thanone select line 215. For example, select line 215 ₀ of block of memorycells 250 ₀ might correspond to the select line 215 ₀ of the memoryarray 200B of FIG. 2B, and the block of memory cells of the memory array200C of FIG. 2C might further include those NAND strings 206 associatedwith select lines 215 ₁-215 _(K) of FIG. 2B. In such blocks of memorycells 250 having NAND strings 206 associated with multiple select lines215, those NAND strings 206 commonly associated with a single selectline 215 might be referred to as a sub-block of memory cells. Each suchsub-block of memory cells might be selectively connected to the bufferportion 240 responsive to its respective select line 215.

FIG. 3A is a schematic of a portion of an array of memory cells andstring drivers as could be used in a memory device of the type describedwith reference to FIG. 1 and depicting a many-to-one relationshipbetween local access lines (e.g., word lines 202) and global accesslines (e.g., global word lines 302).

As depicted in FIG. 3A, a plurality of memory blocks 250 might havetheir local access lines (e.g., word lines 202) commonly selectivelyconnected to a plurality of global access lines (e.g., global word lines302). Although FIG. 3A depicts only memory blocks 250 ₀ and 250 _(L)(Block 0 and Block L), additional memory blocks 250 might have theirword lines 202 commonly connected to global word lines 302 in a likemanner. Similarly, although FIG. 3A depicts only four word lines 202,memory blocks 250 might include fewer or more word lines 202.

To facilitate memory access operations to specific memory blocks 250commonly coupled to a given set of global word lines 302, each memoryblock 250 might have a corresponding set of block select transistors 354in a one-to-one relationship with their word lines 202. Control gates ofthe set of block select transistors 354 for a given memory block 250might have their control gates commonly coupled to a corresponding blockselect line 356. As discussed with reference to FIG. 4 , the blockselect lines 356 (e.g., block select lines 356 ₀-356 _(L) might eachrepresent multiple independent conductors, each connected to arespective control gate of a multi-gate transistor.

For memory block 250 ₀, word line 202 ₀₀ might be selectively connectedto global word line 302 ₀ through block select transistor 354 ₀₀, wordline 202 ₁₀ might be selectively connected to global word line 302 ₁through block select transistor 354 ₁₀, word line 202 ₂₀ might beselectively connected to global word line 302 ₂ through block selecttransistor 354 ₂₀, and word line 202 ₃₀ might be selectively connectedto global word line 302 ₃ through block select transistor 354 ₃₀, whileblock select transistors 354 ₀₀-354 ₃₀ are responsive to control signalsreceived on block select line 356 ₀. For memory block 250 _(L), wordline 202 _(0L) might be selectively connected to global word line 302_(L) through block select transistor 354 _(0L), word line 202 _(1L)might be selectively connected to global word line 302 ₁ through blockselect transistor 3541L, word line 202 _(2L) might be selectivelyconnected to global word line 302 ₂ through block select transistor 354_(2L), and word line 202 _(3L) might be selectively connected to globalword line 302 ₃ through block select transistor 354 _(3L), while blockselect transistors 354 _(0L)-354 _(3L) are responsive to control signalsreceived on block select line 356 _(L). The block select transistors 354for a block of memory cells 250 might collectively be referred to as astring driver, or simply driver circuitry.

FIG. 3B is a schematic of a portion of one example of a string driver ascould be used in a memory of the type described with reference to FIG. 1. The portion of the string driver of FIG. 3B depicts one transistor,e.g., block select transistor 354 _(YX), responsive to a control signalnode, e.g., block select line 356 _(X), and connected between a voltagenode, e.g., a global word line 302 _(Y), configured to supply a voltagelevel, and load node, e.g., local word line 202 _(YX), configured toreceive that voltage level. For example, the block select transistor 354_(YX) might represent the block select transistor 354 ₁₀ having controlgates connected to the block select line 356 ₀ and connected between theglobal word line 302 ₁ and the local word line 202 ₁₀ of the block ofmemory cells 250 ₀. The block select transistor 356 _(YX) might be ahigh-voltage junction-gate field-effect transistor or JFET. As discussedwith reference to FIG. 4 , the block select line 356 _(X) mightrepresent multiple independent conductors.

FIG. 3C is a schematic of a portion of another example of a stringdriver as could be used in a memory of the type described with referenceto FIG. 1 . The portion of the string driver of FIG. 3C depicts twotransistors, e.g., block select transistor 354 _(YX) and block selecttransistor 354 _(Y(X+1)). Block select transistor 354 _(YX) isresponsive to a control signal node, e.g., block select line 356 _(X),and connected between a voltage node, e.g., a global word line 302 _(Y),configured to supply a voltage level, and load node, e.g., local wordline 202 _(YX), configured to receive that voltage level. For example,the block select transistor 354 _(YX) might represent the block selecttransistor 354 ₁₀ having control gates connected to the block selectline 356 ₀ and connected between the global word line 302 ₁ and thelocal word line 202 ₁₀ of the block of memory cells 250 ₀.

Block select transistor 354 _(Y(X+1)) is responsive to a control signalnode, e.g., block select line 356 _(X+1), and connected between avoltage node, e.g., the global word line 302 _(Y), configured to supplya voltage level, and load node, e.g., local word line 202 _(Y(X+1)),configured to receive that voltage level. For example, the block selecttransistor 354 _(Y(X+1)) might represent the block select transistor3541L having control gates connected to the block select line 356 _(L)and connected between the global word line 302 ₁ and the local word line202 _(1L) of the block of memory cells 250 _(L). The block selecttransistors 356 _(YX) and 356 _(Y(X+1)) might each be high-voltageJFETs. As discussed with reference to FIG. 4 , the block select lines356 _(X) and 356 _(X+1) might each represent multiple independentconductors.

FIG. 4 is a plan view of transistors 454 ₀ and 454 ₁ in accordance withan embodiment. The transistors of FIG. 4 might be represented by aschematic such as depicted in FIG. 3C. In FIG. 4 , the transistors 454(e.g., transistors 454 ₀ and 454 ₁) each include an active area 460(e.g., active areas 460 ₀ and 460 ₁, respectively) of a semiconductor,e.g., a conductively-doped semiconductor. Each transistor might beformed between a respective first contact 466 ₀ or 466 ₁, e.g., forconnection to a respective voltage node, such as a global access line,and a respective second contact 468 ₀ or 468 ₁, e.g., for connection toa respective load node, such as a local access line. Such transistorsmight be responsive to control signals received on conductors 464, e.g.,conductors 464 ₀-464 _(G), which might be connected to (and might form)at least a portion of the control gates of one or more transistors. Theconductors 464 might be independent from one another. For example, eachconductor 464 might be configured to receive a control signal, e.g., anapplied voltage level, that is independent of control signals for eachremaining conductor 464. Collectively, the conductors 464 ₀-464 _(G)might represent a block select line 356. The active areas 460 ₀ and 460₁ might extend to a second pair of adjacent transistors (not fullydepicted in FIG. 4 ) sharing the first contacts 466 ₀ and 466 ₁, such asshown by the phantom line corresponding to a conductor 464 _(0′) of thesecond pair of adjacent transistors with the structure of the secondpair of adjacent transistors being a mirror image of the transistors 454₀ and 454 ₁.

FIGS. 5A-12D are cross-sectional views of the transistors of FIG. 4 atvarious stages of fabrication in accordance with an embodiment. FIGS.5A, 6A, 7A, 8A, 9A, 10A, 11A and 12A are cross sections taken along theline A-A in FIG. 4 . FIGS. 5B, 6B, 7B, 8B, 9B, 10B, 11B and 12B arecross sections taken along the line B-B in FIG. 4 . FIGS. 5C, 6C, 7C,8C, 9C, 10C, 11C and 12C are cross sections taken along the line C-C inFIG. 4 . FIGS. 5D, 6D, 7D, 8D, 9D, 10D, 11D and 12D are cross sectionstaken along the line D-D in FIG. 4 .

Although the cross sections of FIGS. 5A, 6A, 7A, 8A, 9A, 10A, 11A and12A depict a portion of the transistor 454 ₀ from one side, thesefigures might further apply to a corresponding cross section of theother side of the transistor 454 ₀, or either side of the transistor 454₁, as both transistors might have a similar, e.g., the same, structureand might be symmetrical on either side of their active areas 460.Although the cross sections of FIGS. 5B, 6B, 7B, 8B, 9B, 10B, 11B and12B depict a portion of the transistor 454 ₀, these figures mightfurther apply to a corresponding cross section of transistor 454 ₁ asboth transistors might have a similar, e.g., the same, structure.Although the cross sections of FIGS. 5C, 6C, 7C, 8C, 9C, 10C, 11C and12C depict a portion of the transistors 454 ₀ and 454 ₁ containing theconductor 464 ₀, these figures might further apply to a correspondingcross section of transistors 454 ₀ and 454 ₁ containing any of theremaining conductors 464 ₁-464 _(G), as such portions of bothtransistors might have a similar, e.g., the same, structure. Althoughthe cross sections of FIGS. 5D, 6D, 7D, 8D, 9D, 10D, 11D and 12D depicta portion of the transistors 454 ₀ and 454 ₁ containing the firstcontacts 466 ₀ and 466 ₁, respectively, these figures might furtherapply to a corresponding cross section of transistors 454 ₀ and 454 ₁containing the second contacts 468 ₀ and 468 ₁, respectively, as suchportions of both transistors might have a similar, e.g., the same,structure.

In FIGS. 5A-5D, a dielectric 572 might be formed overlying (e.g., on) asubstrate 570. The substrate 570 might comprise silicon, such asmonocrystalline silicon, or other semiconductor material. Thesemiconductor 570 might have a conductivity type, such as a p-typeconductivity. The substrate 570 might be below the peripheral circuitry226 of FIG. 2B for certain embodiments whose transistors are to beformed as a portion of that peripheral circuitry. Alternatively, thesubstrate 570 might include the memory array 200B of FIG. 2B for certainembodiments whose transistors are to be formed above that memory array.

The dielectric 572 might be formed of one or more dielectric materials.For example, the dielectric 572 might comprise, consist of, or consistessentially of an oxide, e.g., silicon dioxide, and/or might comprise,consist of, or consist essentially of a high-K dielectric material, suchas aluminum oxides (AlO_(x)), hafnium oxides (HfO_(x)), hafnium aluminumoxides (HfAlO_(x)), hafnium silicon oxides (HfSiO_(x)), lanthanum oxides(LaO_(x)), tantalum oxides (TaO_(x)), zirconium oxides (ZrO_(x)),zirconium aluminum oxides (ZrAlO_(x)), or yttrium oxide (Y₂O₃), as wellas any other dielectric material.

A conductor 574 might be formed overlying (e.g., on) the dielectric 572.The conductor 574 might be formed of one or more conductive materials.The conductor 574 might comprise, consist of, or consist essentially ofconductively doped polycrystalline silicon (polysilicon) and/or mightcomprise, consist of, or consist essentially of metal, such as arefractory metal, or a metal-containing material, such as a refractorymetal silicide or a metal nitride, e.g., a refractory metal nitride, aswell as any other conductive material. As an example, the conductor 574might contain tungsten or aluminum. For one embodiment, where thetransistors are to be formed under a memory array, the conductor 574might include tungsten. For another embodiment, where the transistorsare to be formed over a memory array, the conductor 574 might includealuminum. In general, conductive materials, e.g., metals, having lowerthermal budgets of formation, might be preferred in situations where thearray of memory cells has already been formed. Such conductive materialsmight have lower thermal budgets of formation relative to conductivematerials, e.g., metals, formed under the array of memory cells.

In FIGS. 6A-6D, the conductor 574 might be patterned to define a firstportion of each control gate of the future transistors. For example, theconductor 574 might be patterned to define lower control gate portions462 ₀-462 _(G) of the future transistor as a first control gate portionof a control gate. A number of control gates for the future transistormight contain G+1 lower control gate portions. The variable G mightrepresent an integer value greater than or equal to one. For someembodiments the variable G might represent an integer greater than orequal to five. The value of the variable G might be determined inresponse to a breakdown characteristic corresponding to the controlgates of the finished transistor. For example, if a breakdown voltagebetween adjacent control gates is X volts, and an expected maximum Vdsis Y volts, the variable G might be selected to be an integer value thatis equal to or greater than Y/X.

Patterning the conductor 574 might include forming a patterned mask (notdepicted) formed overlying (e.g., on) the conductor 574 to expose areasof the conductor 574 for removal. The mask might represent a mask formedusing a photolithographic process. Photolithographic processes are oftenused to define a desired pattern in integrated circuit fabrication. In aphotolithographic process, a photoresist layer might be formed on thesurface of the in-process device. The photoresist layer might contain aphoto-sensitive polymer whose ease of removal is altered upon exposureto light or other electromagnetic radiation. To define the pattern, thephotoresist layer might be selectively exposed to radiation and thendeveloped to expose portions of the underlying layer. In a positiveresist system, the portions of the photoresist layer exposed to theradiation are photosolubilized and a photolithographic mask is designedto block the radiation from those portions of the photoresist layer thatare to remain after developing. In a negative resist systems, theportions of the photoresist layer exposed to the radiation arephotopolymerized and the photolithographic mask is designed to block theradiation from those portions of the photoresist layer that are to beremoved by developing.

The exposed areas of the conductor 574 might be removed, e.g.,anisotropically, to define the lower control gate portions 462 ₀-462_(G). For example, a reactive ion etch process might be used to removeportions of the conductor 574 not covered by the patterned mask. Themask might subsequently be removed, e.g., by ashing or otherwiseremoving the photoresist material.

In FIGS. 7A-7D, the dielectric 572 might be extended, such as by formingadditional dielectric material overlying, e.g., on, the lower controlgate portions 462 ₀-462 _(G) and overlying, e.g., on, the dielectric 572of FIGS. 6A-6D. A semiconductor material 576 might then be formedoverlying, e.g., on, the dielectric 572 as depicted in FIGS. 7A-7D. Thesemiconductor material 576 might comprise silicon, such asmonocrystalline, amorphous or polycrystalline silicon, or othersemiconductor material, such as silicon germanium (SiGe). Othersemiconductor materials might include indium zinc oxide (commonlyreferred to as InZnO or InZO), zinc oxide (ZnO), indium gallium zincoxide (commonly referred to as InGaZnO or IGZO), molybdenum disulfide(MoS₂), molybdenum diselenide (MoSe₂), tungsten disulfide (WS₂),tungsten diselenide (WSe₂), graphene, carbon nanotubes, etc. Thesemiconductor material 576 might have a first conductivity type, such asa p-type conductivity. The semiconductor material 576 might beconductively doped during or after formation. To produce a p-typeconductivity, the dopant species might include ions of boron (B) oranother p-type impurity. For example, a semiconductor material 576 mightbe conductively doped during formation by adding diborane (B₂H₆) to thereaction gases of a CVD process to form the semiconductor material 576in order to incorporate sufficient boron into the semiconductor material576 to achieve a desired threshold voltage of the future transistor,e.g., a dopant concentration of undoped to 2E18/cm³ might be used. As analternate example, a semiconductor material 576 might be conductivelydoped after formation by implanting one or more dopant species into thesemiconductor material 576. As is well understood in the art, suchimplantation might commonly involve acceleration of ions directed at asurface of the semiconductor material 576. To produce an n-typeconductivity, the dopant species might include ions of arsenic (As),antimony (Sb), phosphorus (P) or another n-type impurity

In FIGS. 8A-8D, the conductively-doped semiconductor material 576 mightbe patterned to define the active areas 460 ₀ and 460 ₁. Patterning ofthe conductively-doped semiconductor material 576 might be performed ina manner similar to that discussed with reference to FIGS. 6A-6D. Afirst source/drain region 578, e.g., a source region, and a secondsource/drain region 580, e.g., a drain region, might be formed in eachof the active areas 460 ₀ and 460 ₁ and might have a second conductivitytype different than the first conductivity type. For example, where thefirst conductivity type is a p-type conductivity, the secondconductivity type might be an n-type conductivity.

Forming the source/drain regions 578 and 580 might include conductivelydoping portions of the active areas 460 ₀ and 460 ₁. For example, thefirst source/drain region 578 and the second source/drain region 580might be formed by implanting one or more dopant species into an activearea 460. To produce an n-type conductivity, a dopant species mightinclude ions of arsenic (As), antimony (Sb), phosphorus (P) or anothern-type impurity. The doping levels of the first source/drain region 578and the second source/drain region 580 might be higher than the dopinglevels of their active area 460. As one example, the doping levels ofthe first source/drain region 578 and the second source/drain region 580might be 2E18-1E21/cm³. Although the first source/drain region 578 andthe second source/drain region 580 are depicted to extend into theactive areas 460 ₀ and 460 ₁ less than their thickness, e.g., asmeasured from a top surface to a bottom surface of the active areas 460as viewed in FIGS. 8B and 8D, for some embodiments, the firstsource/drain region 578 and the second source/drain region 580 mightextend the full thickness of the active areas 460 ₀ and 460 ₁.

In FIGS. 9A-9D, a dielectric 582 might be formed overlying, e.g., on,the structure of FIGS. 8A-8D. The dielectric 582 might be formed of oneor more dielectric materials, such as discussed with reference todielectric 572.

In FIGS. 10A-10D, conductive vias 463 might be formed in the dielectric582 to be in contact with the lower control gate portions 462 ₀-462_(G). One or more conductive vias 463 might be in contact with eachlower control gate portion 462. Conductive vias 586 might further beformed, e.g., concurrently with the conductive vias 463, in thedielectric 582 to be in contact with the first source/drain regions 578and second source/drain regions 580. For example, openings might beformed in the dielectric 582 to each individually expose a portion ofthe first source/drain region 578, the second source/drain region 580,or a lower control gate portion 462 ₀-462 _(G), and then the openingsmight be filled or lined with conductive material. For one embodiment,the conductive vias 463 and 586 might each contain conductively-dopedpolysilicon, e.g., an n-type conductively-doped polysilicon, althoughother conductive materials might also or alternatively be used. As oneexample, the doping levels of the conductive vias 463 and 586 might be2E18-1E21/cm³. The conductive vias 463 might form a second and a thirdcontrol gate portion of the control gates of the future transistor,e.g., side control gate portions, and might be referred to as such.

In FIGS. 11A-11D, a conductor 588 might be formed overlying (e.g., on)the dielectric 582. The conductor 588 might be formed of one or moreconductive materials. The conductor 588 might comprise, consist of, orconsist essentially of conductively doped polysilicon and/or mightcomprise, consist of, or consist essentially of metal, such as arefractory metal, or a metal-containing material, such as a refractorymetal silicide or a metal nitride, e.g., a refractory metal nitride, aswell as any other conductive material. As an example, the conductor 588might contain tungsten or aluminum. For one embodiment, where thetransistors are to be formed under a memory array, the conductor 588might include tungsten. For another embodiment, where the transistorsare to be formed over a memory array, the conductor 588 might includealuminum. In general, conductive materials, e.g., metals, having lowerthermal budgets of formation, might be preferred in situations where thearray of memory cells has already been formed. Such conductive materialsmight have lower thermal budgets of formation relative to conductivematerials, e.g., metals, formed under the array of memory cells.

In FIGS. 12A-12D, the conductor 588 might be patterned to define afourth portion of each control gate of the transistor. For example, theconductor 588 might be patterned to define conductors, or upper controlgate portions, 464 ₀-464 _(G) of the transistors, as well as the firstcontacts 466 ₀-466 ₁, and the second contacts 468 ₀-468 ₁. Patterningthe conductor 588 might be performed in a manner such as described withreference to the patterning of the conductor 574.

FIGS. 12A-12D depict transistors each having multiple independentcontrol gates surrounding (e.g., lower, side and upper surfaces of) anactive area 460. Collectively, a lower control gate portion 462 adjacentan active area 460, its corresponding side control gate portions 463adjacent that active area 460, and its corresponding upper control gateportion 464 adjacent that active area, might define one control gate 465(e.g., of control gates 465 ₀₀-465 _(G0) of FIG. 12A) of a transistor454 containing that active area 460. As one example, the lower controlgate portion 462 ₀ adjacent a bottom surface of the active area 460 ₀,the side control gate portions 463 adjacent left and right surfaces ofthe active area 460 ₀, and the upper control gate portion 464 ₀ adjacenta top surface of the active area 460 ₀, might collectively define acontrol gate 465 ₀₀ of the transistor 454 ₀. For each control gate 465,its lower control gate portion 462 might be in a plane parallel to aplane containing its upper control gate portion 464, and its sidecontrol gate portions 463 might be in different planes that are eachorthogonal to the planes of the lower control gate portion 462 and theupper control gate portion 464.

For one embodiment, lengths of the control gates (e.g., as measured in aleft-to-right direction of FIG. 12A) might be 0.15 μm with a spacingbetween adjacent control gates of 0.05 μm. The control gates might bespaced apart from the surfaces of the active area 460 by 0.04 μm, e.g.,by a dielectric material. For some embodiments, the lower portions ofthe control gates might be spaced apart from the lower surface of theactive area 460 by a greater distance than the side and upper surfaces.For example, the lower portions of the control gates might be spacedapart from the lower surface of the active area 460 by 0.14 μm. Theactive areas 460 might have a cross section of 0.07 μm by 0.07 μm.Although specific examples of dimensions are provided, such dimensionsare not essential, and other dimensions could be used in response todesired operational characteristics, or in response to advancements inthe ability to reliably define smaller device dimensions.

As depicted in FIG. 12B, the distance (e.g., lateral distance) d1between the first source/drain region 578 and a nearest control gate,e.g., a control gate having lower control gate portion 462 ₀ and uppercontrol gate portion 464 ₀, might be different than the distance (e.g.,lateral distance) d2 between the second source/drain region 580 and anearest control gate, e.g., a control gate having lower control gateportion 462 _(G) and upper control gate portion 464 _(G). In particular,it might be desired to have different lengths of active area between thesource side and the drain side of the transistor 454 ₀ and a nearestcontrol gate for each, e.g., due to an expected voltage drop across thetransistor 454 ₀. For example, the distance d1 might be larger than thedistance d2 in view of an expectation that the voltage level of thevoltage node be higher than the voltage level of the load node.

The embodiment of FIGS. 12A-12D might connect an upper control gateportion 464 and its corresponding lower control gate portion 462 to asame signal line of the block select line 356. Alternatively, a signalline of the block select line 356 might be connected to a particularcontrol gate portion of a control gate, e.g., an upper control gateportion 464 or a lower control gate portion 462, and each remainingcontrol gate portion of the control gate might be connected to thatsignal line only through their connection to the particular control gateportion.

Although the embodiment depicted with reference to FIGS. 5A-12D depictsthree conductive vias 463 extending from a lower control gate portion462 to an upper control gate portion 464 on two sides of an active area460, alternate embodiments might utilize more or fewer conductive vias463 to connect a lower control gate portion 462 to a corresponding uppercontrol gate portion 464. The conductive vias 463 might be in contactwith a majority of the length of each lower control gate portion 462 andupper control gate portion 464, as measured in a left-to-right directionon FIG. 12A. Furthermore, although the embodiment depicted withreference to FIGS. 5A-12D depicts multiple conductive vias 463 extendingfrom a lower control gate portion 462 to an upper control gate portion464 on two sides of an active area 460, alternate embodiments mightutilize a single conductive via 463′ on each side of the active area toconnect a lower control gate portion 462 to a corresponding uppercontrol gate portion 464. FIG. 13 is a cross-sectional view of atransistor of FIG. 4 in accordance with a further embodiment taken alongline A-A of FIG. 4 , where the conductive via 463′ extends across amajority of the lengths of the lower control gate portion 462 and uppercontrol gate portion 464, as measured in a left-to-right direction onFIG. 13 . For some embodiments, the conductive via 463′ might extend afull length of the lower control gate portion 462 or upper control gateportion 464, and further embodiments might extend beyond the full lengthof the lower control gate portion 462 or upper control gate portion 464.Although the cross-section of FIG. 13 depicts one side of the transistor454 ₀, this cross-section might equally apply to the other side of thetransistor 454 ₀, or to either side of the transistor 454 ₁.

In addition, although the embodiment depicted with reference to FIGS.5A-12D depicts the lower control gate portions 462 extending betweenadjacent transistors, e.g., between transistors 454 ₀ and 454 ₁ asdepicted in FIG. 12C, alternate embodiments might separate lower controlgate portions 462 of adjacent transistors. FIG. 14 is a cross-sectionalview of transistors of FIG. 4 in accordance with a further embodimenttaken along line C-C of FIG. 4 . FIG. 14 depicts an example where thetransistor 454 ₀ has a lower control gate portion 462 ₀₀ separated froma lower control gate portion 462 ₀₁ of transistor 454 ₁. Such separatedlower control gate portions 462 might be defined during the patterningof the conductor 574 as discussed with reference to FIGS. 6A-6D.Although the cross-section of FIG. 14 depicts the lower control gateportions 462 ₀₀ and 462 ₀₁, this cross-section might equally apply toany of the lower control gate portions 462 as they might all have asimilar, e.g., the same, structure.

Furthermore, although the embodiment depicted with reference to FIGS.5A-12D depicts the active areas 460 surrounded by control gate portions462, 463 and 464, e.g., having control gate portions adjacent surfacesof an active area 460 in four planes, various embodiments may onlypartially surround the active areas 460, e.g., having control gateportions adjacent surfaces of an active areas 460 in fewer than fourplanes. FIGS. 15A-15E are cross-sectional views of transistors of FIG. 4in accordance with various embodiments having control gate portionsadjacent surfaces of the active areas 460 in fewer than four planes.Directional terms in the description of FIGS. 15A-15E will be from thepoint of view of a viewer of the figures.

In FIG. 15A, the transistors 454 have control gate portions adjacentsurfaces, e.g., a top surface and a side surface, of each of the activeareas 460 in two planes. For example, for each active area 460, theupper control gate portion 464 ₀ is adjacent an upper surface of theactive areas 460 extending in a plane, e.g., a horizontal plane, abovethe active areas 460; and the respective side control gate portions 463are adjacent side surfaces of the active areas 460 extending in planes,e.g., vertical planes, adjacent side surfaces of the active areas 460,e.g., a right side surface of active area 460 ₀ and a left side surfaceof active area 460 ₁. Note that such embodiments having side controlgate portions 463 on one side of an active area 460 might alternativelybe on a same side of each active area 460. For example, the side controlgate portions 463 might be adjacent a right side of each active area 460₀ and 460 ₁, or adjacent a left side of each active area 460 ₀ and 460₁. In addition, embodiments might stagger on which side a side controlgate portion 463 is placed for different control gates. For example, theside control gate portion 463 might be adjacent the right side surfaceof the active area 460 ₀ for the upper control gate portion 464 ₀ asdepicted in FIG. 15A, and a side control gate portion 463 might beadjacent the left side surface of the active area 460 ₀ for the uppercontrol gate portion 464 ₁.

In FIG. 15B, the transistors 454 have control gate portions adjacentsurfaces, e.g., a top surface and a side surface, of each of the activeareas 460 in two planes similar to that discussed with reference to FIG.15A. However, while the side control gate portions 463 of FIG. 15A aredepicted to extend beyond an entirety of the thickness of the activeareas 460, e.g., as measured from the top surface to the bottom surfaceof the active areas 460, the side control gate portions 463 in FIG. 15Bare depicted to extend along less than the entirety of the thickness ofthe active areas 460.

In FIG. 15C, the transistors 454 have control gate portions adjacentsurfaces of each of the active areas 460 in three planes, e.g., a topsurface and both side surfaces. Similar to the discussion of FIG. 15A,the side control gate portions 463 might extend the entirety of thethickness of the active areas 460, which might include extending beyondthe bottom surface of the active areas 460 as depicted, or they mightextend less than the entirety of the thickness of the active areas 460as discussed with reference to FIG. 15B.

In FIG. 15D, the transistors 454 have control gate portions adjacentsurfaces of each of the active areas 460 in three planes, e.g., a topsurface, one side surface and a bottom surface. For example, for eachactive area 460, the upper control gate portion 464 ₀ is adjacent anupper surface of the active areas 460 extending in a plane, e.g., ahorizontal plane, above the active areas 460; the respective sidecontrol gate portions 463 are adjacent side surfaces of the active areas460 extending in planes, e.g., vertical planes, adjacent side surfacesof the active areas 460, e.g., a left side surface of active area 460 ₀and a right side surface of active area 460 ₁; and the lower controlgate portions 462 ₀₀ and 462 ₀₁ are adjacent a lower surface of theactive areas 460 extending in a plane, e.g., a horizontal plane, belowthe active areas 460. Although the embodiment of FIG. 15D depicts lowercontrol gate portions 462 of different active areas 460 separated fromone another, the lower control gate portions could utilize a singleconductor such as depicted in FIG. 12C. Although not necessary, such anembodiment using a single conductor for the lower control gate portions462 might connect both the lower control gate portion 462 and the uppercontrol gate portion 464 to a same signal line of the block select line356. Alternatively, such an embodiment might connect the signal line ofthe block select line 356 to only one of the upper control gate portion464 and the lower control gate portion 462.

In FIG. 15E, the transistors 454 have control gate portions adjacentsurfaces of each of the active areas 460 in two planes, e.g., a topsurface and a bottom surface. The embodiment of FIG. 15E utilizes asingle conductor for the lower control gate portions 462. For example,for each active area 460, the upper control gate portion 464 ₀ isadjacent an upper surface of the active areas 460 extending in a plane,e.g., a horizontal plane, above the active areas 460; and the lowercontrol gate portion 462 ₀ is adjacent a lower surface of the activeareas 460 extending in a plane, e.g., a horizontal plane, below theactive areas 460. The upper control gate portion 464 ₀ and the lowercontrol gate portion 462 ₀ might be commonly connected to a signal line1556 ₀ of a block select line 356. Each remaining signal line 1556₁-1556 _(G) of the block select line 356 might be similarly commonlyconnected to respective pairs of upper control gate portions 464 andlower control gate portions 462 as indicated.

FIG. 16 conceptually depicts connection of a portion of a string drivercircuitry connected to access lines of multiple blocks of memory cellsin accordance with an embodiment. For example, a first string driver1695 ₀ might have transistors (not enumerated in FIG. 16 ) correspondingto conductors 464 ₀₀-464 _(G0) and connected between first contacts 466,e.g., first contacts 466 _(X), 466 _(X+1), and 466 _(X+2), andcorresponding second contacts 468, e.g., second contacts 468 _(X0), 468_((X+1)0), and 468 _((X+2)0), respectively, and a second string driver1695 ₁ might have transistors (not enumerated in FIG. 16 ) correspondingto conductors 464 ₀₁-464 _(G1) and connected between first contacts 466,e.g., first contacts 466 _(X), 466 _(X+1), and 466 _(X+2), andcorresponding second contacts 468, e.g., second contacts 468 _(X1), 468_((X+1)1), and 468 _((X+2)1), respectively. The transistors of thestring drivers 1695 ₀ and 1695 ₁ might correspond to the transistors 454depicted in FIGS. 4 and 12A-12D, for example.

The second contacts 468 _(X0), 468 _((X+1)0), and 468 _((X+2)0) of thefirst string driver 1695 ₀ might be connected to word lines 202 _(X0),202 _((X+1)0), and 202 _((X+2)0), respectively, of a block of memorycells 250 ₀. The word lines 202 _(X0), 202 _((X+1)0), and 202 _((X+2)0)might represent only a portion of word lines of the block of memorycells 250 ₀. For example, the block of memory cells 250 ₀ might includeN+1 word lines 202 such as depicted in FIG. 2A, and the word lines 202_(X0), 202 _((X+1)0), and 202 _((X+2)0) of the block of memory cells 250₀ might correspond to word lines 202 _(X), 202 _(X+1), and 202 _(X+2),respectively, of FIG. 2A.

The second contacts 468 _(X1), 468 _((X+1)1), and 468 _((X+2)1) of thesecond string driver 1695 ₁ might be connected to word lines 202 _(X1),202 _((X+1)1), and 202 _((X+2)1), respectively, of a block of memorycells 2501. The word lines 202 _(X1), 202 _((X+1)1), and 202 _((X+2)1)might represent only a portion of word lines of the block of memorycells 2501. For example, the block of memory cells 2501 might includeN+1 word lines 202 such as depicted in FIG. 2A, and the word lines 202_(X1), 202 _((X+1)1), and 202 _((X+2)1) of the block of memory cells2501 might correspond to word lines 202 _(X), 202 _(X+1), and 202_(X+2), respectively, of FIG. 2A.

The string drivers 1695 ₀ and 1695 ₁ might be a portion of theperipheral circuitry 226 of FIG. 2C. For example, the string driver 1695₀ might be formed under (e.g., at least partially under) the word lines202 _(X0), 202 _((X+1)0), and 202 _((X+2)0) of the block of memory cells250 ₀. Similarly, the string driver 1695 ₁ might be formed under (e.g.,at least partially under) the word lines 202 _(X1), 202 _((X+1)1), and202 _((X+2)1) of the block of memory cells 2501. Alternatively, thestring driver 1695 ₀ might be formed over (e.g., at least partiallyover) the word lines 202 _(X0), 202 _((X+1)0), and 202 _((X+2)0) of theblock of memory cells 250 ₀, and the string driver 1695 ₁ might beformed over (e.g., at least partially over) the word lines 202 _(X1),202 _((X+1)1), and 202 _((X+2)1) of the block of memory cells 2501.

To activate a string driver 1695, or any of its correspondingtransistors, e.g., transistor 454 ₀ of FIG. 4 , a reference potential,e.g., ground, 0 V or Vss, might be applied to each of the conductors 464₀-464 _(G) as the transistor might be a normally-on transistor, whetherthe active area 460 has a p-type or n-type conductivity.

To deactivate a string driver 1695, or any of its correspondingtransistors, e.g., transistor 454 ₀ of FIG. 4 , one or more positivevoltage levels (e.g., for a p-type active area) or one or more negativevoltage level (e.g., for an n-type active area) having sufficientmagnitude might be applied to one or more of the conductors 464 ₀-464_(G). For some embodiments, the voltage level applied to the conductor464 ₀ has a magnitude that is greater than or equal to the respectivemagnitudes of the voltage levels applied to the remaining conductors 464₁-464 _(G). For further embodiments, the voltage level applied to theconductor 464 _(Q) has a magnitude that is greater than or equal to therespective magnitudes of the voltage levels applied to the remainingconductors 464 _(Q+1)-464 _(G). for each value of Q satisfying therelationship 0<=Q<=G−1. For still further embodiments, a voltagedifference between the voltage level applied to conductor 464 _(Q) andthe voltage level applied to conductor 464 _(Q+1) is less than or equalto a voltage difference between the voltage level applied to conductor464 _(Q+1) and the voltage level applied to conductor 464 _(Q+2) foreach value of Q satisfying the relationship 0<=Q<=G−2.

As one example of deactivating a transistor of the type depicted in FIG.4 where G=8, where the first contact 466 is configured to receive 30V,and where the second contact 468 is at 0 V, the conductor 464 ₀ might beconfigured to receive 30 V, the conductor 464 ₁ might be configured toreceive 30V, the conductor 464 ₂ might be configured to receive 28V, theconductor 464 ₃ might be configured to receive 25V, the conductor 464 ₄might be configured to receive 20V, the conductor 464 ₅ might beconfigured to receive 15V, the conductor 464 ₆ might be configured toreceive 10V, the conductor 464 ₇ might be configured to receive 5V, andthe conductor 464 ₈ might be configured to receive 0V.

FIG. 17 is a perspective view of a transistor 454 in accordance with anembodiment. Like numbered elements in FIG. 17 correspond to thedescription as provided with respect to FIGS. 5A-12D. In the embodimentof FIG. 17 , the variable G is equal to four, such that the transistor454 of FIG. 17 includes five control gates 465 ₀-465 ₄. FIG. 17 furtherdepicts an embodiment where the first source/drain region 578 and thesecond source/drain region 580 extend a full thickness of the activearea 460.

CONCLUSION

Although specific embodiments have been illustrated and describedherein, it will be appreciated by those of ordinary skill in the artthat any arrangement that is calculated to achieve the same purposemight be substituted for the specific embodiments shown. Manyadaptations of the embodiments will be apparent to those of ordinaryskill in the art. Accordingly, this application is intended to cover anyadaptations or variations of the embodiments.

What is claimed is:
 1. A transistor, comprising: an active area having afirst conductivity type; a first source/drain region in the active areaand having a second conductivity type different than the firstconductivity type; a second source/drain region in the active area andhaving the second conductivity type; and a plurality of control gatesbetween the first source/drain region and the second source/drainregion, wherein each control gate of the plurality of control gatescomprises: a respective first control gate portion overlying a firstside of the active area; and a respective second control gate portionconnected to its respective first control gate portion and adjacent to asecond side of the active area orthogonal to the first side of theactive area.
 2. The transistor of claim 1, wherein the active areaextends in a first direction from the first source/drain region to thesecond source/drain region, wherein the respective first control gateportion of each control gate of the plurality of control gates extendsin a second direction orthogonal to the first direction, and wherein therespective second control gate portion of each control gate of theplurality of control gates extends from its respective first controlgate portion in a third direction orthogonal to the first direction andorthogonal to the second direction.
 3. The transistor of claim 1,wherein the respective second control gate portion of each control gateof the plurality of control gates is adjacent to the second side of theactive area for less than an entirety of a thickness of the active area.4. The transistor of claim 1, wherein each control gate of the pluralityof control gates further comprises a respective third control gateportion connected to its respective first control gate portion andadjacent to a third side of the active area orthogonal to the first sideof the active area and opposite the second side of the active area. 5.The transistor of claim 4, wherein the respective third control gateportion of each control gate of the plurality of control gates extendsfrom its respective first control gate portion in the third direction.6. The transistor of claim 4, wherein the third side of the active areais opposite the second side of the active area and is orthogonal to thefirst side of the active area.
 7. The transistor of claim 1, wherein therespective second control gate portion of each control gate of theplurality of control gates comprises a different conductive materialthan its respective first control gate portion.
 8. A transistor,comprising: an active area having a first conductivity type; a firstsource/drain region in the active area and having a second conductivitytype different than the first conductivity type; a second source/drainregion in the active area and having the second conductivity type; and aplurality of control gates between the first source/drain region and thesecond source/drain region, wherein each control gate of the pluralityof control gates comprises: a respective first control gate portionoverlying a first side of the active area; and a respective secondcontrol gate portion connected to its respective first control gateportion and underlying a second side of the active area opposite thefirst side of the active area.
 9. The transistor of claim 8, whereineach control gate of the plurality of control gates further comprises arespective third control gate portion connected to its respective firstcontrol gate portion and extending between its respective first controlgate portion and its respective second control gate portion adjacent athird side of the active area orthogonal to the first side of the activearea and orthogonal to the second side of the active area.
 10. Thetransistor of claim 9, wherein each control gate of the plurality ofcontrol gates further comprises a respective fourth control gate portionconnected to its respective first control gate portion and extendingbetween its respective first control gate portion and its respectivesecond control gate portion adjacent a fourth side of the active areaorthogonal to the first side of the active area, orthogonal to thesecond side of the active area, and opposite the third side of theactive area.
 11. The transistor of claim 9, wherein the respective thirdcontrol gate portion of a particular control gate of the plurality ofcontrol gates comprises one or more conductive vias.
 12. The transistorof claim 8, wherein each control gate of the plurality of control gatesis independent of each remaining control gate of the plurality ofcontrol gates.
 13. A memory, comprising: an array of memory cellscomprising a plurality of strings of series-connected memory cells; aplurality of access lines, wherein each access line of the plurality ofaccess lines is commonly connected to a control gate of a respectivememory cell of each string of series-connected memory cells of theplurality of strings of series-connected memory cells; and a stringdriver comprising a plurality of transistors, wherein each transistor ofthe plurality of transistors is selectively connected to a respectiveaccess line of the plurality of access lines; wherein a first transistorof the plurality of transistors comprises: a first control gate adjacenta first active area, wherein the first control gate comprises: a firstcontrol gate portion adjacent a first side of the first active area; anda second control gate portion connected to the first control gateportion and adjacent a second side of the first active area differentthan the first side of the first active area; and a second control gateadjacent the first active area, wherein the second control gatecomprises: a third control gate portion adjacent the first side of thefirst active area; and a fourth control gate portion connected to thethird control gate portion and adjacent the second side of the firstactive area; wherein a second transistor of the plurality of transistorscomprises: a third control gate adjacent a second active area, whereinthe third control gate comprises: a fifth control gate portion adjacenta first side of the second active area; and a sixth control gate portionconnected to the fifth control gate portion and adjacent a second sideof the second active area different than the first side of the secondactive area; and a fourth control gate adjacent the second active area,wherein the fourth control gate comprises: a seventh control gateportion adjacent the first side of the second active area; and an eighthcontrol gate portion connected to the seventh control gate portion andadjacent the second side of the second active area; wherein the firstcontrol gate portion and the fifth control gate portion are respectiveportions of a first conductor; and wherein the third control gateportion and the seventh control gate portion are respective portions ofa second conductor.
 14. The memory of claim 13, wherein the firstcontrol gate portion, the third control gate portion, the fifth controlgate portion, and the seventh control gate portion are in a first plane.15. The memory of claim 14, wherein the second control gate portion andthe fourth control gate portion are in a second plane orthogonal to thefirst plane, and wherein the sixth control gate portion and the eighthcontrol gate portion are in a third plane orthogonal to the first planeand parallel to the second plane.
 16. The memory of claim 14, whereinthe second control gate portion, the fourth control gate portion, thesixth control gate portion, and the eighth control gate portion are in asecond plane parallel to the first plane.
 17. The memory of claim 13,wherein the second control gate portion and the sixth control gateportion are respective portions of a third conductor, and wherein thefourth control gate portion and the eighth control gate portion arerespective portions of a fourth conductor.
 18. The memory of claim 13,wherein the second control gate portion is separated from the sixthcontrol gate portion by a dielectric material, and wherein the fourthcontrol gate portion is separated from the eighth control gate portionby the dielectric material.
 19. The memory of claim 13, furthercomprising: wherein the first control gate further comprises a ninthcontrol gate portion adjacent to a third side of the first active areadifferent than the first side of the first active area and differentthan the second side of the first active area, wherein the ninth controlgate portion is connected to the first control gate portion andextending between the first control gate portion and the second controlgate portion; wherein the second control gate further comprises a tenthcontrol gate portion adjacent to the third side of the first activearea, wherein the tenth control gate portion is connected to the thirdcontrol gate portion and extending between the third control gateportion and the fourth control gate portion; wherein the third controlgate further comprises an eleventh control gate portion adjacent to athird side of the second active area different than the first side ofthe second active area and different than the second side of the secondactive area, wherein the eleventh control gate portion is connected tothe fifth control gate portion and extending between the fifth controlgate portion and the sixth control gate portion; and wherein the fourthcontrol gate further comprises a twelfth control gate portion adjacentto the third side of the second active area, wherein the twelfth controlgate portion is connected to the seventh control gate portion andextending between the seventh control gate portion and the eighthcontrol gate portion.
 20. The memory of claim 19, further comprising:wherein the first control gate further comprises a thirteenth controlgate portion adjacent to a fourth side of the first active areadifferent than the first side of the first active area, different thanthe second side of the first active area, and different than the thirdside of the first active area, wherein the thirteenth control gateportion is connected to the first control gate portion and extendingbetween the first control gate portion and the second control gateportion; wherein the second control gate further comprises a fourteenthcontrol gate portion adjacent to the fourth side of the first activearea, wherein the fourteenth control gate portion is connected to thethird control gate portion and extending between the third control gateportion and the fourth control gate portion; wherein the third controlgate further comprises an fifteenth control gate portion adjacent to afourth side of the second active area different than the first side ofthe second active area, different than the second side of the secondactive area, and different than the third side of the second activearea, wherein the fifteenth control gate portion is connected to thefifth control gate portion and extending between the fifth control gateportion and the sixth control gate portion; and wherein the fourthcontrol gate further comprises a sixteenth control gate portion adjacentto the fourth side of the second active area, wherein the sixteenthcontrol gate portion is connected to the seventh control gate portionand extending between the seventh control gate portion and the eighthcontrol gate portion.